This invention relates to valve assemblies, and in particular, to a fire damper assembly.
Building and fire codes require that fire dampers be placed in specified heating, ventilation and air conditioning (HVAC) ducts. Such dampers are normally open to allow air flow therethrough and closed in the event of a fire to prevent smoke, toxic gases, heat and the fire itself from being transmitted through the duct. Also, fire dampers help smother a fire by sealing off the area of a blaze and preventing fresh air from circulating through a structure's duct work to the flames.
Blades in such fire damper assemblies may be held in an open position by heat responsive linkage means such as the bimetallic link shown in the McCabe U.S. Pat. No. 4,146,048 which shows a pair of hinged blades in a butterfly damper restrained in an open position until a predetermined air temperature is reached.
Other prior art fire dampers include those shown in the Gerlitz U.S. Pat. No. 2,825,275 and the Coe U.S. Pat. No. 2,912,920 which, unlike the present invention, are normally closed and spring open in the event of a fire to dissipate heat and smoke. The devices shown therein both utilize fusible links which melt at predetermined temperatures and release the damper blades to spring open.
However, prior art fire damper assemblies normally have spring means for urging the blades to a closed position and hinging means separate from the spring means. This additional complexity tends to reduce the reliability of such devices because dirt and grease can accumulate thereon over long periods of time with the damper assembly in its normal position. Another deficiency of the hinge mechanisms of certain prior art dampers, such as that shown in the Richterkessing et al U.S. Pat. No. 3,009,475, is that they do not provide a positive and sealable connection between the two blades and are therefore susceptible to leakage. Further, many prior art fire dampers have only 2 positions, wide open or fully closed, and do not allow for varying the air flow therethrough.